With a haste buff you gain an additional attack with your mainhand weapon at your highest attack bonus, wich is doubled in a Time stand still maneuver. Overall this gives you a maximum of 24 attacks:

Mainhand: 38/38/38/38/38/38/33/33/33/33/28/28/23/23

Offhand: 38/38/38/38/38/38/33/33/28/28

If you have a good healer in your party you can increase your damage output tremendously by placing a viscious enchant on your weapons instead of one elemental damage enchant. You realy need a good healer because this deals up to 24d6 points of damage to you, but increases your damage output at the same time by up to another 24d6.

This would be 24d8+492+168d6 wich is (if all attacks hit and without crits) an avarage of 1188 damage.

If dm allows flaws pick up shakey in illiterite for two more bounus feats

In fights with a lot of movement, where you aren't able to make full attacks you can use maneuvers wich increase your damage on one strike like f.e. Feral Death Blow.

Even better are either the Sudden Leap boost wichs allows you to move in a swift action, so that you still can take a full attack action, or a Pouncing Charge wich also allows a full attack.

Your low Reflex and Will saves can be avoided with Diamond Mind counters (Moment of Perfect Mind, Action Before Thought), and with Iron Heart Surge you can remove negative conditions.

OBS: Weapon Supremacy gives a +5 boost in only 1 attack after the first (players Choice).
There's no feats to buy Weapon supremacy and Improved Critical in the level 20.
Slashing Flurry only gives 1 extra attack. Not 1 for each weapon.

Low damage against creatures with high damage reductions.
Lack of ranged options.
Difficult to fight invisible, hit and run and others diferent oriented style of combat enemies.
Weak against enemies with high AC.
Items needed for full usage.

Against higher enemies, it could be worth to change the elemental damage enchants with a wounding enchantment on your weapons, wich can deal upt to 24 Con damage to your target in one round. This means a loss of 240 hit points for a creature with 20 hit dice.

Furthermore a vampiric enchantment on your weapons could be a nice choice wich may heal you for up to 24d6 points of damage in one round.

Instead of a Human you may prefer to take an Orc instead, which gives you a +4 to Strength. Over all you lose one feat, which should be Improved Critical which you can replace by a keen weapon enchant, or just accept the loss of the increased critrange.